Timing audio and video signals with coincidental markers

Abstract

A method for timing audio and video component signals of a television signal with coincidental markers generates a field pulse every Nth field of the televison signal at the transmitter. The duration of the field pulse is approximately one video field, and is ued to enable an audio tone generator for the one video field and to switch a distinctive video signal, such as a flat video signal, into the video component signal for the one video field. At the receiver the two component signals are input through a synchronizer to a waveform display device, such as an oscilloscope, to observe the time differential between the two markers in the audio and video component signals. The audio component signal is delayed by the synchronizer until the markers are again in time conicidence as at the transmitter.

What is claimed is: 
     
       1. A method of timing the audio and video components of a television signal that are transmitted from a transmitter to a receiver over different paths comprising the steps of: periodically generating a distinctive video signal and an audio tone signal in time coincidence as coincidental markers for insertion into the respective components for transmission by the transmitter over the different paths;   displaying the audio and video components at the receiver as waveform on a display device;   observing on the display device a time delay difference between the respective coincidental markers of the components; and   delaying one of the components at the receiver by an amount equal to the time delay difference so that the coincidental markers are in time coincidence.   
     
     
       2. An apparatus for generating coincidental markers at a transmitter for timing of the audio and video portions of a television signal at a receiver comprising: means for generating a periodic reference pulse;   means for generating from the periodic reference pulse an audio pulse and a video pulse in time coincidence; and   means for generating an audio tone signal in response to the audio pulse and a distinctive video signal in response to the video pulse as coincidental markers.   
     
     
       3. An apparatus as recited in claim 2 wherein the periodic reference pulse generating means comprises: a color frame counter that is incremented by a clock synchronized to a master sync signal of the television signal and is reset at the end of a video color frame of the television signal; and   means for generating the periodic reference pulse from the count output of the color frame counter once per color frame.   
     
     
       4. An apparatus as recited in claim 3 wherein the audio and video pulse generating means comprises: a binary counter for counting the periodic reference pulses from the periodic reference pulse generating means; and   a decoder, having as inputs the count of the binary counter and the count of the color frame counter, to output the audio and video pulses for a duration of one video field of the television signal each time the count of the binary counter reaches a predetermined value so that the audio and video pulses occur in time coincidence once every Nth video field.   
     
     
       5. An apparatus as recited in claim 2 further comprising: means at the receiver for detecting a time delay difference between the audio tone signal and the distinctive video signal; and   means for delaying one of the components according to the time delay difference.